The dominant commercial process for the manufacture of adipic acid involves the air-oxidation of cyclohexane to form a mixture of cyclohexanol and cyclohexanone, which is subsequently oxidized with nitric acid to form a mixture of carboxylic acids, including adipic acid.
Another process for making adipic acid involves the hydrocarboxylation of pentenoic acids and their esters. Pentenoic acids and their esters, and in particular 3-pentenoic acid, are available from butadiene and butadiene derived feedstocks by metal catalyzed hydrocarboxylation. Such processes have the potential of providing high yield, high rate, low pollution processes for the manufacture of adipic acid. In the hydrocarboxylation of 3-pentenoic acid and its esters, higher levels of branched products are formed than are normally encountered in the hydrocarboxylation of simple olefins. Burke (U.S. Pat. No. 4,788,333) has disclosed that, for the production of adipic acid by the hydrocarboxylation of pentenoic acids, high linear selectivity is obtained when an iodide-promoted rhodium catalyst is employed in conjunction with selected halocarbon solvents.
Burke discloses in U.S. Pat. No. 4,939,298, the branched diacids can be separated from the product adipic acid and then isomerized to adipic acid by heating in the presence of carbon monoxide and an iodide or bromide promoted rhodium catalyst.
The most commonly used promoters for metal catalyzed hydrocarboxylation also promote the conversion of pentenoic acids and esters to gamma-valerolactone. This material can also be separated from the product adipic acid and hydrocarboxylated to adipic acid as described in Burke EPO published application 90107900.4, but there are costs and yield losses associated with such processes.
Craddock et al (U.S. Pat. No. 3,816,489) disclose a process "for the production of terminal carboxylic acids" from "ethylenically unsaturated compounds" by hydrocarboxylation "in the presence of catalyst compositions essentially comprising iridium compounds and complexes, together with an iodide promoter in critical proportions". In U.S. Pat. No. 3,816,488 Craddock et al disclose that similar results can be obtained using rhodium catalysts. The preferred reaction solvents are monocarboxylic acids having 2 to 20 carbon atoms.
European Patent Application No. 0 511 126 A2 published Oct. 28, 1992 discloses the preparation of adipic acid by hydrocarboxylation of pentenoic acid using an iridium catalyst promoted with an iodide.
U.S. Pat. No. 3,090,807 (Illing et al.) discloses a process for the isomerization of aliphatic carboxylic acids by heating with carbon monoxide "in the presence of (a) a metal carbonyl and (b) chlorine, bromine, or iodide and/or one or more compounds of one or more of these halogens as catalysts, and preferably in the presence of (c) an activator and (d) water." Suitable metal carbonyls are those of the 6th, 7th and 8th group of the periodic system. Metal carbonyls of the iron group, especially cobalt and nickel, are preferred. The most preferred is nickel. The isomerization of adipic acid to 2-methylglutaric acid and 2,3-dimethylsuccinic acid is discussed and exemplified in Examples 1 and 6. In Example 1 nickel carbonyl activated by bismuth iodide is employed while in Example 6 cobalt acetate activated by bismuth oxide and hydrogen iodide is employed. Although the process is said to be suitable for the isomerization of linear acids to branched acids and branched acids to linear acids, there is no mention of the isomerization of branched C6-diacids to adipic acid.
Taiwan Patent 047769 to Burke discloses a process for the preparation of adipic acid by the carbonylation of certain lactones including gamma-valerolactone in the presence of a rhodium catalyst and an iodide or bromide promoter.
U.S. Pat. No. 3,625,996 (Union Oil) discloses a process for the preparation of olefinic acids or esters from diacids or esters by contacting with a complex catalyst comprising a Group VIII noble metal and a ligand from the group consisting of organic phosphines, arsines and stiblines. Iridium is mentioned as a catalyst.
U.S. Pat. No. 3,592,849 (Union Oil) discloses a process for the "preparation of acids from their anhydrides with isomerization of the acid by contacting the anhydride with a catalyst comprising a complex of a Group VIII metal and a biphyllic ligand" at elevated temperature. The process produces carboxylic acid, olefin and CO. The biphyllic ligands are selected from organic compounds containing arsenic, antimony, phosphorus or bismuth in a trivalent state. Iridium is mentioned as a group VIII metal that may be employed.
U.S. Pat. No. 5,077,447 (Henkel) discloses a process for making olefins by reaction of a mixture of carboxylic acid and a carboxylic anhydride in the presence of a Group VIII metal or copper containing catalyst. Iridium is mentioned as a group VIII metal that may be employed. In Example 8, an iridium catalyst is employed to convert decanoic acid to 1-nonene.